A member of the community liaison committee for the twinning of Nova Scotia's Highway 101 near Windsor says the plan to cross the Avon River represents a compromise that considers environmental and First Nations concerns while also satisfying federal fisheries laws.

The twinning project between Falmouth and Three Mile Plains has already started. But there are concerns from some people in the Windsor area about the aboiteau planned for the river, because it will allow salt water into the lake next to town and lower water levels.

Darren Porter, a member of the community liaison committee, said the method being recommended for the crossing is the most feasible option to meet federal fisheries laws for fish passage and follows extensive consultation and scientific study.

Porter, a commercial fisherman, said the aboiteau design would include two openings, a little more than a metre wide each, that would allow water to flow through at a controlled rate with the tide.

There would also be a large swinging iron gate between the two slots to serve as flood protection for the town and beyond, something Porter said is essential because of the aging mechanics in the existing causeway.

"Right now we're at a huge flood risk," he said.

The aboiteau would be built next to the current causeway. The causeway's gates, which currently prevent tidal waters from coming into the lake, would be opened.

Some people, including the town's mayor, have expressed concerns about what changes to the lake could mean for future development, water access to fire departments and the apparent suddenness of the news.

But Porter said no one should be surprised. He said municipal officials have been kept aware of discussions for the project as the committee has done its work.

A common counter to the current proposal has been the suggestion of using fish ladders, but Porter said it would require five or six different fish ladders to accommodate the various species and there simply isn't enough water to facilitate that approach.

"As soon as you put in a fish ladder you have to pump water up the fish ladder because the lake is lower than the ocean."

Fish-pass laws have seen the lake next to town essentially drained for two and a half months each year in order to draw fish out to sea to spawn.

While the current proposal will lower the lake from the current high-water mark, Porter said it would prevent it from going completely dry, instead fluctuating each day with the tides.

Getting to this point has required compromise, and Porter acknowledged not everyone will be happy about it. The change will be a problem for the local canoe club, whose members have worried about remaining viable. Porter, himself, will lose a long-time fishing spot to the location of the new crossing.

But the federal fishery laws aren't negotiable, and Porter said others are making compromises, too.

He noted people who pushed for the removal of the causeway or to build a bridge as the second crossing have compromised with the idea of the aboiteau.

Angie Gillis, director of environment and natural resources at the Confederacy of Mainland Mi'kmaq, was brought in as part of a scientific working group, which included Porter as a representative of the commercial fisheries and Acadia University scientists.

Gillis said the priority for her group was a continuous fish passage that was not manually operated. Coming into talks, Gillis was adamant the crossing had to be a bridge. But she said things were put into perspective during talks and the need for compromise was stressed to meet the needs of others, such as farmers up the river.

"We'll take the fact they're going to allow fish passage. It's not that we're endorsing the fact that it's not a bridge," she said. "Take the wins where you can get them."

Gillis said being included in the process made compromise easier.

"We're finally being allowed to have our science included in a lot of decisions that are made. Twenty or 30 years ago, this structure would have been put up, there would have been no fish passage, it would have been manually operated and we wouldn't have had a say."

Porter said he's hoping a community meeting on Oct. 10 will help people with concerns understand what's happening and why it's happening. Keeping the lake lower than it is now means salt water won't make it into the ditches and dykes used by farmers, for example, he said. It will also have no effect on Ski Martock, which uses freshwater for its operations.

Porter said he was as sceptical as anyone at the start of the work, but he said he's been impressed by the way the team has worked together to use local, traditional and academic knowledge to reach a compromise that will work for most people.

"It was hard when it started — because not everybody always gets along — [but] then by the end of it we all were on the same page and we said, 'This is the best we can do with what we have to meet everybody's needs.'"